Location determination is becoming an increasingly important capability for some electronic devices, such as cellular telephones, personal digital assistants (PDA's), and portable computers, as well as other devices. Separate from the direct benefits associated with knowing one's current location, many venders are introducing or contemplating location based services or solicitations, which can be selectively made available to the user of an electronic device, and which are dependent upon the device's current and/or anticipated location. Still other location based features and/or capabilities, relative to portable electronic devices, are being mandated by governmental agencies. One such example of a location based feature, which has been mandated by the US Federal Communication Commission (FCC), includes a feature known as E911.
In conjunction with supporting the various location based features and services, many different technologies and techniques have been developed, which are intended to support making a location determination. Each technology and/or technique has a varying degree of accuracy, time, supporting infrastructure requirements, and rates of success. For example, various technologies generally make use of terrestrial based reference locations, such as one or more base stations; non-terrestrial based reference locations, such as one or more orbiting satellites; or a combination of the two. Many techniques make use of a measure of a position relationship relative to multiple reference locations, whether it is distance, direction, or both, which can be directly or indirectly identified or inferred. In many instances the position relationship can be derived from an analysis of a received reference signal originating from multiple reference locations. Examples of various techniques and/or determination approaches include the use of global positioning systems that can typically make use of a constellation of space-based satellites. Several such techniques can include a mobile station-assisted assisted global positioning system, a mobile station-based assisted global positioning system, and/or an autonomous global positioning system, where the space-based satellites represent reference locations from which a mobile subscriber's location can be derived using various triangulation/trilateration approaches. Additional examples include positioning systems that alternatively use the same or similar triangulation/trilateration approaches, but rely upon ground based reference locations, which can take the form of beacons, cell towers, base stations, or other signal sources, each having a known or an inferable position.
While the use of space based reference locations as part of a global positioning system is becoming increasingly popular, there are some instances when systems that primarily or exclusively use space based reference locations can be frustrated or impractical. Generally in order to make use of a reference location, whether it is space-based or land-based, the mobile station needs to be able to receive a reference signal therefrom. In some instances, signals from a particular reference location may be unavailable due to interference from other signal sources or due to various absorption/reflection of a reference signal. For example, reference signals from space based locations can sometimes be unavailable within certain structures as the types of signals used by the signal sources will have a varying ability to penetrate into a building or other obstructing structures.
Consequently even with the more widespread support for and availability of space based global positioning systems, there is still a need for terrestrial based systems, that can supplement or be used in place of the space based systems in at least some circumstances in order to give greater assurances of meeting location determining requirements, such as the requirements under the E911 regulations.
As such, alternative reference signals from other suitable signal sources having a known location may need to be available in order to enable an alternative manner or approach of determining a location of the mobile station. One such signal source can include cellular base stations. However, in order to provide enough information with which a location can be determined, a signal from which relative positioning information, such as range or direction, from multiple sources having a known location is needed. With cellular base stations, signals from nearby base stations can interfere with other more remotely located base stations, thereby making it more difficult to receive a signal from one of the more remotely located signal sources, as well as making it more difficult to derive the needed signal characteristics from the received signal for use in determining a location.
In some instances a particular signal source may be unsuitable, for which any attempts to receive a signal from the particular source might result in failure, unnecessary delay, and/or wasted resources. In other instances a signal source suitable for deriving a signal for use in determining a location may not be readily known to the mobile subscriber as part of any other readily maintained list of reference signal source sites, but which may be most suitable for supporting a location determination.
Consequently, a method which sends lists of base stations that could be used to identify or supplement other known lists of suitable and/or unsuitable signal sources for use in receiving a reference signal for use in making a location determination would be beneficial.